WA Police believe an increase in extremist activity is inevitable, revealing that a "small number" of homegrown radicals are being monitored because of their hard-line views.
Security Operations unit Supt Mike Bell would not comment on individuals or the groups they supported but said the number under surveillance was likely to grow as conflicts such as the jihadist insurgency in Iraq and Syria fanned the flames of radicalism here.
"WA has traditionally been very stable . . . but we are a global community and things that happen on the other side of the world which never used to affect us - they do now," he said. "As a result, we are monitoring for an increase in extremist activity. It is inevitable, unfortunately."
The warning came as Federal Attorney-General George Brandis revealed new intelligence suggesting Australians fighting in overseas conflicts were being trained in domestic terrorism.
"There is evidence they (Australians) are trained in terrorist trade-craft to perform acts of domestic terrorism in the event that they return either to their home countries or go elsewhere after they have been in theatre," Senator Brandis told the ABC's 7.30 program.
"So that is a new and very alarming development.
"That's why I've said several times now that this is the biggest threat to Australian domestic security in many years."
Australian Federal Police have also revealed arrest warrants have been issued for two Australians believed to be fighting in Iraq with the banned terrorist group the Islamic State.
Khaled Sharrouf and Moh-amed Elomar are believed to have been involved in beheadings and other atrocities. Last week, they reportedly posted photos of themselves holding up the severed heads of opponents.
Tony Abbott said yesterday that Australians who went abroad to fight foreign battles could expect to be jailed if they returned.
"I have a very strong message for any Australian who is thinking of going overseas to engage in guerilla warfare, jihadism, anything of this nature - don't do it," the Prime Minister said.
"It is a serious crime. If you come back to Australia, you will be arrested, you will be charged, you will be jailed."
ASIO recently confirmed that as many as 100 Australians were fighting overseas and about 10 had returned. None of those was believed to be living in WA.
Supt Bell said information from the public was essential for police to stay on top of emerging threats from within the local community.